In U.S. Pat. No. 4,004,731 means is shown for circulating the heat from a fireplace to the circulating air plenum of a central heating system of a house or the like. Accordingly, in the event of fuel shortage, auxiliary wood or coal can be burned in the fireplace, and the heat distributed throughout the entire house by the blower motor of the furnace.
Any heating device which is incorporated into a building structure should meet stringent safety requirements, relating, for example, to the maximum permissible temperature of the outer wall of the heater. If the temperature of the outer wall is excessive, a substantial spatial clearance of the heat ducts from the combustible wooden parts of the house should be maintained.
With modern heating devices using gas, oil or electricity, a thermostat can be used to control the temperature. However, a solid fuel fire is not as readily controllable in this manner, although an automatic damper can be used. In the case of an electrical power failure, an automatic damper may cease to function, and the thermostat and blowers will also cease operation, which may result in an excessive temperature increase in the air circulation conduit surrounding the fireplace.
A power failure is, of course, a prime time when one might wish to have a fire in the home, with the result that a fire hazard may be created by an extreme increase of temperature in the duct work adjacent the furnace, in the event that the hot duct is in essential contact with flammable materials.
Accordingly, there is a need for a safe zero-clearance fireplace unit in thermal connection with the house ductwork. By the term "zero-clearance," it is meant that the fireplace unit can be installed in essential contact with flammable materials such as studs in the wall of the house, wallboard, or the like.
One alleged zero-clearance fireplace is illustrated by U.S. Pat. No. 3,888,231. Such a construction has a drastically reduced heat efficiency, since a great amount of the heat transferred through the fireplace walls is dissipated up the chimney flue by a current of cold air drawn from outdoors into the outer chamber of the device to cool it, and to lower the temperature of the skin of the outer housing.
Also, some free-standing stoves have had a double wall construction to attempt to reduce the temperature of the outer wall. However, they still give rise to fire hazards.
In accordance with this invention, a solid fuel furnace is provided which is safe enough to be enclosed into the structure of the building, or even placed inside of a small, closed space such as a closet or a small utility area.
The solid fuel furnace may be in the form of a decorative fireplace, or a central heating furnace in an enclosed part of the house. The apparatus of this invention may be used in combination with another conventional gas, oil, electric, or solar heating device, or a heat pump, as well as an optional air conditioning unit.